[alsa-devel] ALSA: SNDRV_PCM_STATE_PAUSED

[Takashi Iwai]

At Thu, 12 Dec 2013 15:08:11 +0900,
JongHo Kim wrote:
> 
> Hi
> I develop ALSA SOC Part and use the tinyalsa library on application space.
> We recently used pause ioctl command(SNDRV_PCM_IOCTL_PAUSE)
> because the music application was needed to pause and resume feature.
> So the music application was achieved to want pause
> and resume feature using the SNDRV_PCM_IOCTL_PAUSE.
> 
> but I found some problem in alsa kernel framework
> 
> The music application process on pause state wake up in 10 seconds
> because the wait time is set by 10 seconds in wait_for_avail function.
> 
> I realized that if the 'runtime->no_period_wakeup' parameter is true,
> the wait_time will be set by the MAX_SCHEDULE_TIMEOUT.
> 
> I had searched other kernel source and library source.
> I added the SNDRV_PCM_INFO_NO_PERIOD_WAKEUP flag at my snd_pcm_hardware
> structure
> and added the SNDRV_PCM_HW_PARAMS_NO_PERIOD_WAKEUP flag at music
> application(use tinyalsa library)
> 
> Result was good!
> The music application perfectly works the pause and resume feature.
> 
> but I have some worries
> if DMA or I2S was stop on the running,
> I can't more see the 'write error (DMA or IRQ trouble?)' message
> and the music application process may be sleep eternally.
> 
> I cautiously recommend next code with a solution to the above worries.
> -------------------------------------------------------------------------------------
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> old mode 100644
> new mode 100755
> index 41b3dfe..3284940
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -1936,6 +1936,8 @@ static int wait_for_avail(struct snd_pcm_substream
> *substream,
>                 case SNDRV_PCM_STATE_DISCONNECTED:
>                         err = -EBADFD;
>                         goto _endloop;
> +               case SNDRV_PCM_STATE_PAUSED:
> +                       continue;
>                 }
>                 if (!tout) {
>                         snd_printd("%s write error (DMA or IRQ trouble?)\n",
> -------------------------------------------------------------------------------------
> 
> I tested code. code works good!
> but I am concerned about the side effects
> please review my idea.

Through my quick glance, this looks like a correct fix.  Could you
submit a proper patch for merging to the upstream?


thanks,

Takashi